AD7750

–15–

REV. 0

Table III. Components for Suggested Class 1 Meter Implementation in Figure 21

Schematic

Designator

Description

Comments

R1

470

Ω, 5%, 1 W

R2

1 k

Ω, 5%, 1/2 W

R3, R4,

100

Ω, 10%, 1/2 W

These registers are required to form part of the antialiasing filtering on the analog inputs;

R7

1 k

Ω, 10%, 1/2 W

they do not perform a voltage-to-current conversion.

R5

1 M

Ω, 5%, 2 W

The choice of R5 determines the attenuation on the voltage channels and hence the meter

rating, e.g., 100 PPKWHR.

R6

1.1 k

Ω, 5%, 1/2 W

Forms part of the Gain Calibration network with R5 and VR1.

R8, R9

500

Ω, 10%, 1/2 W

VR1

100

Ω, 10/15 Turn

This potentiometer is used to perform the Gain Calibration of the meter. Attenuation of

830 to 900—see Applications section.

C1

470 nF, 250 V ac

C2

100

µF, 24 V dc

C3, C4

33 pF

C5, C6,

330 nF

Forms part of the antialiasing filters on the analog inputs.

C9, C10

33 nF

C7, C11

10

µF, 10 V

C8, C12

10 nF

Z1

1N750

D1, D2

1N4007

D3

LED

D4, D5

IR LEDS

XTAL

3.579545 MHz

MOV

V250PA40A

Metal Oxide Varistor–Harris Semiconductor.